A girl received a piggyback heart transplant as a toddler, and the donor organ was removed 10 years later after her own healed. The technique may be useful in developing other types of heart therapy.

In an unprecedented feat, British surgeons implanted a donor heart in a dying toddler whose own heart was too weak to sustain life, then removed it 10 years later after the girl's own heart had fully recovered.

The technique is unlikely to become widespread because of the severe shortage of pediatric donor hearts, but it suggests that better mechanical assist devices that take some or all of the load off a diseased heart could allow time for weakened hearts to heal themselves.

The procedure, reported online Monday in the medical journal Lancet, shows that "the heart has reparative capabilities that we suspected it might have, but for which we have really lacked a great deal of proof," said Dr. Douglas Zipes of Indiana University, a former president of the American College of Cardiology. "We need to understand better how it does it, capitalize on that and be able to use it in routine therapy."

There have been cases in which a second heart was implanted, then failed "and the patients were able to go on for a while with the native heart," said Dr. Matthias Loebe, director of thoracic transplantation and assist devices at the Baylor College of Medicine, one of the leading U.S. centers for heart surgery in children. "But there has never been anything similar to this reported in the literature. That's impressive."

As the journal article recounts: In July 1995, Hannah Clark was 2 years old and suffering from dilated cardiomyopathy, in which the heart becomes weakened and enlarged and cannot pump blood efficiently. The problem is most often caused in young children by genetics or viruses, and affects 1.2 to 1.4 children per 100,000. The prognosis is normally very poor.

Noted heart surgeon Dr. Magdi Yacoub of Imperial College London and Harefield Hospital grafted a donor heart, obtained from a 5-month-old infant, in parallel to Hannah's own heart -- allowing it to take over the bulk of pumping duty, a procedure known as a heterotopic heart transplant. The procedure required substantial doses of immunosuppressive drugs to prevent the heart from being rejected.

The heart functioned efficiently, and Hannah was soon able to lead a normal life, but the drugs began to produce their own problems -- allowing the development of a virus-related cancer called Epstein-Barr virus-associated post-transplant lymphoproliferative disorder.

The cancer was suppressed with courses of powerful drugs, but it kept recurring, and surgeons reduced the dose of anti-rejection drugs to help Hannah's body fight it.

By February 2006, the reduced doses of immunosuppressive drugs were interfering with the donor heart's function: Hannah was near kidney failure, was having difficulty breathing and at one point her family was told she had less than 12 hours to live.

Yacoub and Dr. Victor Tsang of the Great Ormond Street Hospital in London decided to remove the donor heart and stop the drugs altogether.

Hannah, now 16, has fully recovered from her cancer, her heart is functioning normally, and she is able to carry out all the activities of a teenage girl.

Today, children with weakened hearts are occasionally treated with an implanted left ventricular assist device, a form of artificial heart that assumes some of the load from the patient's heart. Such devices are typically left in for a few months to a year or two.

That Hannah's piggybacked heart could be successfully removed after 10 years is "remarkable," said Dr. Kathy Magliato, director of women's cardiac services at St. John's Hospital in Santa Monica and a spokeswoman for the American Heart Assn.

The family, which lives in Mountain Ash near Cardiff, Wales, appeared at a London news conference Monday. Hannah burst into tears when a journalist asked her how the surgery had changed her life.

"Thanks to this operation [removal of the heart], I've now got a normal life just like all my friends," she said. She added that she cherished every moment and that she now plays sports and has a part-time job working with animals, which would have been impossible before she stopped taking the transplant drugs.

Hannah's mother, Liz, praised the family whose daughter provided the donor heart: "They lost a child, we've gained a child. How can I ever thank them?"